Bears' Hibernation Linked To Unusual Changes In Their Gut Microbes

When preparing to hibernate each year, bears gorge on food to pack on fat, all while avoiding health consequences often associated with obesity in humans. Now, researchers have found that the bears' shifting metabolic status is associated with significant changes in their gut microbes -- including specialized summer gut microbiota that takes in more energy from food.

"The restructuring of the microbiota into a more avid energy harvester during summer, which potentially contributes to the increased adiposity (fat) gain without impairing glucose metabolism, is quite striking," Fredrik Bäckhed, lead author from the University of Gothenburg in Sweden, said in a news release.

Previously, Bäckhed and his colleagues found that the composition of gut microbiota can influence the amount of energy harvested from the diet. For instance, microbiota shifts in people who are obese and in those with type 2 diabetes. Now, however, researchers were curious to learn whether changes to the microbiota might also be important for wild hibernating brown bears.

For their study, researchers analyzed fecal samples from wild bears collected during hibernation and in their active period. In general, hibernation microbiota showed reduced diversity; however, researchers also found changes in several metabolites responsible for lipid metabolism, including triglycerides, cholesterol, and bile acids.

In order to further investigate whether those changes ultimately drive the shift in metabolism, the researchers transferred the bears' summer and winter microbiota into germ-free mice in the lab. While mice with the summer microbiota showed greater weight and fat gain than those with the winter microbiota, there were no differences seen in their glucose metabolism.

Furthermore, researchers found that the mice also showed some similarities to the bears, meaning the bears' seasonal metabolic status had been partially transferred to the rodents via those microbes. This suggests the microbiota play a much larger role in switching over the hibernating animals' metabolism and cold adaptation than previously thought.

Researchers say their findings, recently published in the journal Cell Reports, may lead to new strategies for managing obesity in humans.

"I think it's too early [to say], as I consider this being very basic science," Bäckhed added in the university's release. "However, if we learn more about which bacteria and the functions that promote and/or protect against obesity [in hibernating bears], we may identify new potential therapeutic targets."